This invention relates generally to the field of measuring an analyte in a liquid medium. More specifically, it relates to an assay for the measurement of a drug of abuse in a biological sample. In particular, the invention relates to a highly sensitive immunoassay method for the detection of amphetamines, methamphetamines, structurally related drugs such as 3,4-methylenedioxymethamphetamine (MDMA) and metabolites of these drugs in biological samples.
The amphetamine analogues of methylenedioxyphenylalkylamines are a series of compounds referred to as xe2x80x9cdesignerxe2x80x9d amphetamines. As represented in FIG. 1, these psychotropic drugs are ring-substituted derivatives chemically related to mescaline. They include methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA, also known as Ecstasy), methylenedioxyethylamphetamine (MDEA), N-methylbenzodioxazolylbutanamine (MBDB) and benzodioxazol-5xe2x80x2-yl-2-butanamine (BDB), the most common of these being MDMA.
MDA has been shown to be the metabolite of both MDMA and MDEA. Several animal studies have shown that MDMA is metabolized by N-demethylation, deamination, O-methylation and O-conjugation to glucuronide and/or sulfate metabolites. Detected in urine are the parent drug (MDMA), 3,4-methylenedioxylamphetamine (MDA), 4-hydroxy-3-methoxymethamphetamine (HMMA), 3-hydroxy-4-methoxymethamphetamine, 4-hydroxy-3-methoxyphenylacetone, 3,4-methylenedioxyphenylacetone and 3,4-dihydroxyphenylacetone. Most of these metabolites are also present in the blood.
Urine and blood are the most commonly studied biological matrices for MDMA, MDA, MDEA and MBDB and are well documented in the literature. Determination of these designer drugs in other biological specimens such as saliva, sweat and hair has been reported more recently. The parent drug is detected in higher concentrations than its metabolites in these matrices.
The abuse of these designer amphetamines is increasing throughout the world, and their detection by screening methods is becoming a more important issue. Zhao, H. et al., J Anal. Toxicology Vol. 25, PD 258-269(2001) found 71% of urine samples from rave party attendees contained MDMA or MDA alone or in combination with amphetamine or other designer amphetamines such as MDEA. Presently there are no commercial immunoassays designed specifically for the detection of these substances, and their detection therefore depends on the relative cross-reactivities they exhibit in the amphetamine or methamphetamine screening method used. In general, the cross-reactivity of the commercially available amphetamine and methamphetamine assays toward many of these compounds is low which suggests the possibility that some positive samples may go undetected.
In testing for drugs of abuse, immunoassays, particularly competitive binding immunoassays, have proven to be especially advantageous. In competitive binding immunoassays, an analyte in a biological sample competes with a labeled reagent, or analyte analog, or tracer, for a limited number of receptor binding sites on antibodies specific for the analyte and analyte analog. Enzymes such a xcex2-galactosidase and peroxidase, fluorescent molecules such as fluorescein compounds, radioactive compounds such as 125I, and microparticles are common labeling substances used as tracers. The concentration of analyte in the sample determines the amount of analyte analog which will bind to the antibody. The amount of analyte analog that will bind is inversely proportional to the concentration of analyte in the sample, because the analyte and the analyte analog each bind to the antibody in proportion to their respective concentrations. The amount of free or bound analyte analog can then be determined by methods appropriate to the particular label being used.
Gas chromatography/mass spectrometry (GC/MS) is highly specific and has been described for the simultaneous detection of MDMA, MDA, amphetamine, methamphetamine, MDEA and their metabolites. GC/MC analysis is usually required for confirmation and verification of the results of an immunological assay or a suspected diagnosis. In this technique, MDMA or designer drugs are extracted in solid phase, then derivatized and analyzed via GC/MS.
In U.S. Pat. No. 5,501,987 issued Mar. 26, 1996, Ordonez et al. describe a dual analyte immunoassay for the determination of amphetamine and methamphetamine using a single labeled binding partner capable of cross reacting at differing sensitivities to antibodies derived from conjugate derivatives of amphetamine and methamphetamine. Calibrators used are prepared by adding d-amphetamine to drug-free, normal human urine.
Quite surprisingly, it has been discovered that a highly specific immunoassay method for the detection of amphetamines, methamphetamines, structurally related drugs such as 3,4-methylenedioxymethamphetamine (MDMA) and their metabolites in urine samples can be achieved by the use of a calibrator comprising a substance selected from the group consisting of methylenedioxy designer amphetamines in drug free, normal human urine and an antibody having specificity for amphetamine or methamphetamine and cross-reactivity with amphetamine analogues of methylenedioxyphenylalkylamines.
In the method of the invention, a sample suspected of containing amphetamine, methamphetamine or a structurally related drug is combined with an antibody having specificity for amphetamine or methamphetamine and a labeled binding partner which can interact with the combination of antibody and its corresponding analyte so as to detect the presence of the analytes at selected cutoff levels either alone or in combination. The particular antibody or antibodies used must have cross-reactivity with amphetamine analogues of methylenedioxyphenylalkylamines. This invention can be used with any type of immunoassay format, e.g., turbidometric agglutination assay, radioimmunoassay, enzyme immunoassay, or fluorescent polarization immunoassay. Especially preferred is the use of the present invention with agglutinometric formats susceptible to an instrumental method for the measurement of the changes brought about by the agglutination reaction. Both manual as well as automated apparatus testing may be suitably employed for such agglutinometric analysis. Typically, automated instrumentation will operate utilizing a multiplicity of reagent containers or reservoirs from which will be pipetted the appropriate amount of each reagent for addition to the sample. For immunoassays such as the subject agglutination assay, this will usually involve at least two such containers; typically, one for an antibody reagent and the other for the microparticles bound with the corresponding ligand. Additional containers or reservoirs may be present in some instruments containing diluent, buffers or other additives for appropriate treatment of the sample.
The clinical analyzer pipettes the onboard reagents and samples into one cuvette where the competitive agglomeration reaction occurs and measurement of the turbidity is made. For example, using the HITACHI 917 analyzer (Roche Diagnostics) and the ABUSCREEN(copyright) OnLine Amphetamines reagent kit (Roche Diagnostics, Cat. No. 1985965), urine sample is pipetted with sample diluent into the cuvette, followed immediately by the appropriate amount of antibody reagent and mixing. An initial spectrophotometer reading is taken. Then the appropriate quantity of microparticle reagent is transferred to the cuvette and the reaction mixed. After a brief incubation, a final turbidity measurement is made. The overall change in turbidity (absorbance) in the reaction is compared to a calibration curve and results reported in ng/ml.
The present invention also encompasses a reagent test kit which comprises, in packaged combination, an antibody specific for amphetamine, an antibody specific for methamphetamine, a complex comprising a ligand of amphetamine or an amphetamine derivative coupled to a labeling moiety, and a calibrator comprising a known amount of a substance selected from the group consisting of methylenedioxy designer amphetamines. Such a test kit provides reagents for an assay with enhanced clinical sensitivity for MDMA and structurally-related compounds.